Role of silicon as a limiting nutrient to Antarctic diatoms: evidence from kinetic studies in the Ross Sea ice-edge zone

Abstract

During the austral summer of 1990 an intense, diatom-dominated, ice-edge phytoplankton bloom in the SW Ross Sea resulted in depletion of silicic acid, nitrate and phosphate to concentrations much lower than is typical for Antarctic surface waters. Silicic acid was depleted to <6 μM within the core of the meltwater field, where biogenic particulate silica concentrations exceeded 20 μmol l-1. 30Si-labeled Si(OH)4 was used to measure uptake rate at concentrations ranging from 1020 μM above ambient. Dependence of the specific uptake rate (V) on the silicic acid concentration conformed well to a Michaelis-Menten saturation model; maximum uptake rates (Vmax) ranged from 0.0022-0.0028 h-1 which corresponds to maximum growth rates of 0.08-0.10 doublings d-1. Half-saturation constants (km) ranged from 1.1-4.6 μM. Results indicate detectable, but weak, substrate limitation of silicic acid uptake rate by the naturally occurring diatom assemblage. -from Authors